| The automobile industry is developing towards the direction of new energy,intelligence and network.With the increasing number of power electronic devices in automobiles,the electromagnetic compatibility of automobiles has become a very important part in the process of automobile development.As the main power source,the electric drive system is the main electromagnetic interference source in new energy vehicles because of its high power and large current,which seriously threatens the safety and reliability of vehicles.Domestic and foreign EMC test standards put forward higher requirements for electric drive system.The electric drive system should carry out EMC radiation emission and conduction emission experiments under the condition that the measuring motor simulates the load.However,the existing EMC test industry lacks the on-load test system that fully meets the standard requirements.Foreign EMC testing enterprises have mastered the relevant technology but have not shared the research results,and the cost of the developed test system is high.China is still in the stage of technological exploration in this field,so it is urgent to carry out the research and development of EMC on-load test system.In addition,the shaft current generated by the power measuring motor enters the darkroom through the wall shaft,which affects the noise at the bottom of the darkroom and the accuracy of the EMC test carried out by the electric drive system.At the same time,the shaft passes through the shielding wall of the darkroom and causes serious electromagnetic leakage.Therefore,this paper mainly conducts electromagnetic simulation research on the electrically driven EMC on-load test system and carries out optimization design on the test system.The main research contents are as follows:(1)The shaft current generated by the dynamometer motor during operation is the main source of electromagnetic interference in the electrically driven EMC on-load test system.This paper introduces the causes and classification of the shaft current generation,and analyzes the path of the shaft current generation.In view of the electromagnetic leakage caused by the destruction of the integrity of the shield,the basic theory of electromagnetic shielding is studied in this paper.Shielding measures are taken from the aspects of electric field shielding and magnetic field shielding to solve the electromagnetic leakage problem,and the quality of the shielding measures is evaluated through the change of the number of shielding effectiveness.(2)Maxwell’s equations are the basis of solving electromagnetic field problems.This paper introduces Maxwell’s equations and related laws in the form of words and integral formulas,and gives the corresponding differential forms.In this paper,the shielding effectiveness is simulated by using the finite element method,and the electromagnetic problems of electrostatic field,constant magnetic field and eddy current field are calculated by taking the tetrahedron grid with four vertices as an example.(3)Based on electric EMC loading test system,to extract the test information and the system structure parameters to build the test bench and half in a 3 d geometric model,through the structure modeling software for 3 d model was simplified and geometry processing,imported into the electromagnetic simulation software for electromagnetic simulation model of the testing system.During the simulation,the interference path of axial current under low frequency and high frequency was determined by applying axial current excitation to view the model surface current vector diagram after simulation.At the same time,axial current excitation and plane wave excitation were applied to study the shielding effectiveness of the system,and it was determined that the circular hole through the wall had better shielding effect than the square hole,and the appropriate hole size corresponding to different frequency bands was obtained.Through electromagnetic simulation,it is found that installing the shielding shield and grounding the test system can improve the shielding efficiency of the test system.(4)According to GB/T 18655-2018 for the actual loading test system for noise test,analyses the reasons of the bottom noise overrun,and on the basis of the combination of electromagnetic simulation results of load test system has been optimized design,finally by installing the shielding cover,in a half internal coupling do insulation processing and optimization measures such as grounding handling in a lower half of the bottom,makes in a half at the bottom of the noise is lower than 5 GB/T 18655-2018 level limit 35 d B(including V/m,verify the validity of the optimization design. |
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